Spectral changes in fluorescence of phycobilisomes in the course of dissociation

Spectral changes in fluorescence of phycobilisomes (PBS) of Anabaena variabilis in 0.9, 0.6, 0.3 and 0.1 M phosphate buffer at different dissociation times were studied at room or liquid N temperature. The room temperature fluorescence emission maximum of intact PBS was at 678 nm, that of completely dissociated PBS at 644 nm. There were 3 bands in the liquid N temperature fluorescence emission spectrum of PBS: F655, F666 and F686, characteristic of C-phycocyanin (C-PC), allophycocyanin (APC) and APC-B, respectively. The relative fluorescence of F686 in intact PBS was very high, and those of F655 and F666 were low. In the course of PBS dissociation, the relative fluorescence of F686 decreased, and those of F655 and F666 increased. In completely dissociated PBS, the relative fluorescences of F655 and F666 were very high, and F686 disappeared. The linkage between APC and APC-B apparently is unstable while that between C-PC and APC is comparatively stable.